1. Field of the Invention
This invention relates to a connecting structure for an electronic part, for example, for connection of a solar cell to a printed wiring board.
2. Description of the Related Art
In an electronic device such as a portable calculator, such electronic parts as a solar cell, an IC chip and a liquid crystal display panel are mounted on a printed wiring board. In this case, it is known that the electronic parts (e.g., solar cell) are attached to terminals of the wiring board by means of an anisotropic conductive adhesive. In general, such an anisotropic conductive adhesive is formed by mixing metallic particles in a hot-melt type insulative adhesive, or mixing thermoplastic resin particles, having their outer peripheral surfaces plated with metal substance, in a hot-melt type insulative adhesive. In either anisotropic conductive adhesive, the hot-melt insulative adhesive is mixed with such an amount of conductive particles that, at the time of thermal compression, the adhesive has electrical conductivity in the direction of thickness and has an insulating property in the direction of the surface (i.e., a direction perpendicular to the direction of thickness). When external terminals of the electronic parts are connected to connection terminals of the wiring board by this anisotropic conductive adhesive, the connection therebetween is ensured by the hot-melt type insulative adhesive contained in the anisotropic conductive adhesive and the electrical conductivity therebetween is provided by the conductive particles mixed in the hot-melt type insulative adhesive.
However, when the electronic part includes a semiconductor element such as a solar cell, if the anisotropic conductive adhesive mixed with metallic particles is used, the metallic particles directly come into contact with the solar cell. In this case, there is a concern that the solar cell formed of a semiconductor such as amorphous silicon may be destroyed. Also, where the anisotropic conductive adhesive mixed with plate resin particles is used, the resin particles, which are soft, may be deformed at the time of the thermal compression. In this case, the particles are flattened and the amount of the hot-melt type insulative adhesive is reduced between the resin particles and the strength of adherence is decreased. Also, the deformed resin particles have a spring-back force, and there is a high possibility that the deformed resin particles are returned to the original shape, while the adhesive is completely hardened. Thus, reliable electrical conductivity is not attained.